Semiconductor device and method of manufacturing same

ABSTRACT

To achieve a semiconductor device equipped with a low ON voltage and high load short circuit withstand trench gate IGBT. A collector region on a back surface of a semiconductor substrate is comprised of a relatively lightly-doped P+ type first collector region and a relatively heavily-doped P++ type second collector region. The P++ type second collector region includes, in plan view, interfaces between a first trench having therein a first linear trench gate electrode and an N+ type emitter region formed on the side surface of the first trench and between a second trench having therein a second linear trench gate electrode and an N+ type emitter region formed on the side surface of the second trench. This enables electrons injected from the surface side of the semiconductor substrate to reach the P++ type second collector region and offset, with them, holes injected from the back surface side of the semiconductor substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a divisional of U.S. application Ser. No. 15/180,988filed on Jun. 13, 2016, which claims benefit of Japanese PatentApplication No. 2015-163357 filed on Aug. 21, 2015 including thespecification, drawings, and abstract is incorporated herein byreference in their entirety.

BACKGROUND

The present invention relates to a semiconductor device and a method ofmanufacturing same, which are suited for use in, for example, asemiconductor device equipped with a trench gate IGBT (insulated gatebipolar transistor).

For example, Japanese Unexamined Patent Application Publication No.2013-140885 (Patent Document 1) discloses an IE (injection enhancement)type trench gate IGBT having a cell formation region comprisedessentially of a first linear unit cell region having a linear activecell region, a second linear unit cell region having a linear holecollector cell region, and a linear inactive cell region therebetween.

Patent Document

[Patent Document 1] Japanese Unexamined Patent Application PublicationNo. 2013-140885

SUMMARY

It is important to design a trench gate IGBT so as not to allow passageof a collector current equal to or greater than a required amount inorder to ensure load short circuit withstand due to the Kirk effect.Reduction in the collector current, however, leads to such a problem asincreases in ON voltage. The load short circuit withstand can be ensuredby increasing the concentration of the collector region, but itdeteriorates switching-off loss performance. There is accordingly ademand for the development of a semiconductor device equipped with atrench gate IGBT capable of overcoming these problems.

Another problem and a novel feature will be apparent from thedescription herein and accompanying drawings.

A semiconductor device according to one embodiment has a collectorregion on the back surface of a semiconductor substrate. The collectorregion is comprised of a relatively lightly-doped P⁺ type firstcollector region and a relatively heavily doped P⁺⁺ type secondcollector region. The P⁺⁺ type second collector region includes, in planview, an interface between a trench having therein a linear trench gateelectrode to be electrically coupled to a gate electrode and an N⁺ typeemitter region famed on the side surface of the trench.

A method of manufacturing a semiconductor device according to the oneembodiment includes the following steps. First, after formation of afirst trench and a second trench with a space therebetween from thesurface of a semiconductor substrate having therein an N⁻ type driftregion, a first linear trench gate electrode is famed in the firsttrench via a first gate insulating film and a second linear trench gateelectrode is formed in the second trench via a second gate insulatingfilm. Then, a P type body layer is formed on the surface side of thesemiconductor substrate and an N⁺ type emitter region is formed on thesurface side of the semiconductor substrate in the P type body layer soas to be contiguous to the side surface of the first trench. Then, afterformation of an interlayer insulating film on the surface of thesemiconductor substrate, a gate electrode to be electrically coupled tothe first linear trench gate electrode and an emitter electrode to beelectrically coupled to the second linear trench gate electrode, the Ptype body layer, and the N⁺ type emitter region are formed on theinterlayer insulating film. After grinding the semiconductor substratefrom the back surface side thereof into a desired thickness, a P typeimpurity is ion-implanted into the back surface side of thesemiconductor substrate to form a P⁺ type first collector region. Then,after patterning of a resist film formed by application on the backsurface of the semiconductor substrate, a P type impurity ision-implanted into the back surface side of the semiconductor substratewith the patterned resist film as a mask to form a P⁺⁺ type secondcollector region. Then, a collector electrode to be electrically coupledto the P⁺ type first collector region and the P⁺⁺ type second collectorregion is formed on the back surface of the semiconductor substrate. TheP⁺⁺ type second collector region includes, in plan view, an interfacebetween the first trench and the N⁺ type emitter region.

According to the embodiment, a semiconductor device equipped with atrench gate IGBT having a low ON voltage and at the same time, high loadshort circuit withstand can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary plan view of a semiconductor device(semiconductor chip) equipped with a trench gate IGBT according to FirstEmbodiment;

FIG. 2 is a partially enlarged fragmentary plan view showing an activeportion of the semiconductor device according to First Embodiment;

FIG. 3 is a fragmentary cross-sectional view taken along the line A-Ashown in FIG. 2;

FIG. 4 is a fragmentary cross-sectional view taken along the line B-Bshown in FIG. 2;

FIG. 5 is a fragmentary cross-sectional view taken along the line C-Cshown in FIG. 2;

FIG. 6 is a partially enlarged fragmentary plan view showing an activeportion of the semiconductor device according to First Embodiment;

FIG. 7 is a partially enlarged fragmentary cross-sectional view showinga linear active cell region according to First Embodiment;

FIG. 8 is a fragmentary cross-sectional view showing a manufacturingstep of a trench gate IGBT according to First Embodiment;

FIG. 9 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 8;

FIG. 10 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 9;

FIG. 11 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 10;

FIG. 12 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 11;

FIG. 13 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 12;

FIG. 14 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 13;

FIG. 15 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 14;

FIG. 16 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 15;

FIG. 17 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 16;

FIG. 18 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 17;

FIG. 19 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 18;

FIG. 20 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 19;

FIG. 21 is a fragmentary cross-sectional view of the trench gate IGBTduring a manufacturing step following that of FIG. 20;

FIG. 22 is a partially enlarged fragmentary plan view showing an activeportion of a semiconductor device according to Modification Example 1 ofFirst Embodiment;

FIG. 23 is a partially enlarged fragmentary plan view showing an activeportion of a semiconductor device according to Modification Example 2 ofFirst Embodiment;

FIGS. 24A and 24B are surface-side and back-surface-side fragmentaryplan views showing a semiconductor device according to ModificationExample 3 of First Embodiment, respectively;

FIG. 25 is a partially enlarged schematic view of the fragmentarycross-section of the semiconductor device according to ModificationExample 3 of First Embodiment;

FIG. 26 is a surface-side fragmentary plan view showing a semiconductordevice according to Modification Example 4 of First Embodiment;

FIG. 27 is a partially enlarged fragmentary plan view showing an activeportion of the semiconductor device according to Modification Example 4of First Embodiment;

FIG. 28 is a partially enlarged fragmentary plan view showing an activeportion of a semiconductor device according to Second Embodiment;

FIG. 29 is a fragmentary cross-sectional view taken along the line D-Dshown in FIG. 28;

FIG. 30 is a graph showing a field intensity distribution during theload short-circuit of an IGBT, using a collector current density as aparameter;

FIG. 31 is a graph showing the relationship of IGBT between a collectorcurrent (Ic) and ON voltage (V_(CE(sat))), using a proportion of anemitter region per unit area as a parameter;

FIG. 32 is a graph showing a field intensity distribution during theload short circuit of an IGBT, using the concentration of a collectorregion as a parameter; and

FIG. 33 is a graph showing a concentration distribution of the collectorregion of an IGBT, using the concentration of the collector region as aparameter.

DETAILED DESCRIPTION

In the following embodiments, a description will be made after dividedinto a plurality of sections or embodiments if necessary for the sake ofconvenience. These sections or embodiments are not independent from eachother unless otherwise particularly specified, but one of them may be amodification example, application example, detailed description,complementary description, or the like of a part or whole of the otherone. In the following embodiments, when a reference is made to thenumber (including the number, value, amount, range, or the like) of acomponent, the number is not limited to a specific number but may bemore or less than the specific number, unless otherwise particularlyspecified or principally apparent that the number is limited to thespecific number.

Further, in the following embodiments, the constituent component(including component step or the like) is not always essential unlessotherwise particularly specified or principally apparent that it isessential. Similarly, in the following embodiments, when a reference ismade to the shape, positional relationship, or the like of theconstituent component, that substantially approximate or analogous to itis also embraced unless otherwise particularly specified or principallyapparent that it is not. This also applies to the above-described number(including number, value, amount, range, or the like).

Embodiments will hereinafter be described in detail based on drawings.In all the drawings for describing the embodiment, members having thesame function will be identified by the same or related referencenumerals and overlapping descriptions will be omitted. When there aretwo or more members (sites) similar to each other, a symbol may be addedto a generic reference numeral to show an individual or specific site.In the following embodiments, any description on the same or similarportion will not be repeated in principle unless otherwise particularlynecessary.

In the drawings used in the embodiments, even cross-sectional views aresometimes not hatched in order to facilitate understanding of them. Onthe other hand, even plan views are sometimes hatched to facilitateunderstanding of them.

In the cross-sectional or plan view, the size of each site does notcorrespond to that of an actual device. To facilitate understanding ofthe drawing, a specific site may be shown in a relatively large size.Even when a cross-sectional view and a plan view correspond to eachother, the size of a specific site may be relatively increased in orderto facilitate understanding of the drawing.

Problems of an IGBT found by the present inventors will next bedescribed in order to clearly show the semiconductor device of thepresent embodiments.

Problem (1)

When an ON signal is input into an IGBT during load short-circuit, thereis a risk of the IGBT being broken down because due to a power supplyvoltage between a collector and an emitter, the current maximum for theIGBT is applied. Particularly, when the field intensity on the backsurface side of the substrate of the IGBT increases due to a Kirkeffect, the field intensity exceeds the critical field intensity,avalanche breakdown occurs, and a great number of carriers are generatedon the back surface side of the substrate. This phenomenon is likely tolead to marked occurrence of a collector current density (refer to FIG.30). When a parasitic bipolar transistor on the back surface of thesubstrate is turned ON, the IGBT is broken down by latch-up. The Kirkeffect is an effective base width increasing phenomenon that occursbecause an injection level becomes high with an increase in collectorcurrent in a bipolar transistor and a base-collector depletion layer istherefore pushed to the collector side. It is also called “base pushouteffect (kirk effect)”

It is therefore important to design the transistor so as to preventapplication of an excess amount of a collector current in order toensure load short circuit withstand.

Reduction in collector current, however, causes such a problem as anincrease in ON voltage (refer to FIG. 31). The term “ON voltage” means acollector voltage (also called “saturation voltage”) necessary forsending a rated current while applying a gate voltage. In order todecrease the ON voltage as much as possible, an increase in collectorcurrent is desired so that there is a trade-off relationship betweenload short circuit withstand and ON voltage. This means that in order toreduce the ON voltage, an increase in collector current is desired, butin order to increase the load short circuit withstand, a decrease incollector current is desired.

Problem (2)

The Kirk effect can be suppressed by increasing the amount of holessupplied from a PN diode on the back surface side of the substrate tooffset electrons and separating the peak position of the field intensityfrom the PN diode on the back surface side of the substrate. An increasein the amount of holes can be achieved by increasing the concentrationof the collector region (refer to FIGS. 32 and 33). The increase in theconcentration of the collector region, however, inevitably increasesresidual carriers on the back surface side of the substrate when theIGBT is switched OFF. These residual carriers may therefore bedischarged by depletion or be caused to disappear by recombination. Thismay become a cause for deteriorating the switching off loss performance.This means that there is a trade-off relationship between load shortcircuit withstand and switching off loss performance.

The present embodiment therefore provides, in order to overcome theabove-described problems, a technology of not deteriorating theswitching off loss performance but achieving a trench gate IGBT having alow ON voltage and at the same time, having high load short circuitwithstand.

(First Embodiment)

The related art of a trench gate IGBT is disclosed, for example, byJapanese Unexamined Patent Application Publication No. 2013-140885.Japanese Unexamined Patent Application Publication No. 2013-140885(Patent Document 1) discloses (1) a planar structure of a cell regionand therearound, (2) a narrow active cell type unit cell and alternatearrangement system, and (3) an active cell two-dimensional thinned-outstructure so that an overlapping portion will not be repeated inprinciple.

<Structure of Trench Gate IGBT>

A semiconductor device including a trench gate IGBT according to FirstEmbodiment will be described referring to FIGS. 1 to 5. FIG. 1 is afragmentary plan view of a semiconductor device (semiconductor chip)equipped with a trench gate IGBT according to First Embodiment. FIG. 2is a partially enlarged fragmentary plan view showing an active portionof the semiconductor device according to First Embodiment. FIGS. 3 to 5are each a fragmentary cross-sectional view of the trench gate IGBTaccording to First Embodiment. FIG. 3 is a fragmentary cross-sectionalview taken along the line A-A shown in FIG. 2; FIG. 4 is a fragmentarycross-sectional view taken along the line B-B shown in FIG. 2; and FIG.5 is a fragmentary cross-sectional view taken along the line C-C shownin FIG. 2.

The trench gate IGBT described herein is a so-called EEGG type trenchgate IGBT having four trench gate electrodes arranged with a spacebetween any two adjacent ones. Two trench gate electrodes arranged atthe center are each electrically coupled to a gate electrode and theother two trench gate electrodes arranged at both ends are eachelectrically coupled to an emitter electrode. The trench gate IGBT ofFirst Embodiment has a breakdown voltage of, for example, about 600 V.

As shown in FIG. 1, a semiconductor chip SC has, on the upper surface atthe periphery thereof, a cyclic guard ring GR and inside thereof,several (one or more) cyclic field plates FP coupled to a cyclicfloating field ring or the like are provided. The guard ring GR and thefield plate FP are each made of a metal film having, for example,aluminum as a main component.

The semiconductor chip SC has, inside the cyclic field plates FP and inthe main portion of an active portion thereof, a cell formation regionCR. The semiconductor chip SC has, on the upper surface of the activeportion thereof, an emitter electrode EE that extends to the vicinity ofthe periphery of the semiconductor chip SC. The emitter electrode EE ismade of a metal film having, for example, aluminum as a main component.The emitter electrode EE has, at the center portion thereof, an emitterpad EP for coupling a bonding wire or the like thereto.

The emitter electrode EE and the field plate FP have therebetween a gatewiring GL. The gate wiring GL has electrical coupling to the gateelectrode GE. The gate wiring GL and the gate electrode GE are each madeof a metal film having, for example, aluminum as a main component. Thegate electrode GE has, at the center portion thereof, a gate pad GP forcoupling a bonding wire or the like thereto.

As shown in FIG. 2, the cell formation region CR has therein linear unitcell regions LC regularly arranged in a first direction (x direction).Each linear unit cell region LC is comprised of a first linear unit cellregion LC1 and a second linear unit cell region LC2 and in FirstEmbodiment, width W1 of the first linear unit cell region LC1 and widthW2 of the second linear unit cell region LC2 are equal or substantiallyequal to each other.

Each first linear unit cell region LC1 is comprised of a linear activecell region LCa at the center and a pair of half-width linear inactivecell regions LCi surrounding it. The linear active cell region LCa andthe linear inactive cell region LCi have therebetween a first lineartrench gate electrode TG1 or a second linear trench gate electrode TG2electrically coupled to a gate electrode (gate electrode GE shown inFIG. 1).

On the other hand, each second linear unit cell region LC2 is comprisedof a linear hole collector cell region LCc located at the center thereofand a pair of half-width linear inactive cell regions LCi surroundingit. The linear hole collector cell region LCc and the linear inactivecell region LCi have therebetween a third linear trench gate electrodeTG3 or a fourth linear trench gate electrode TG4 electrically coupled tothe emitter electrode EE.

The width Wa of the linear active cell region LCa and the width We ofthe linear hole collector cell region LCc are narrower than the width Wiof the linear inactive cell region LCi. Thus, the trench gate IGBT inFirst Embodiment is a so-called “narrow active cell type unit cell”.

The linear active cell region LCa or the linear hole collector cellregion LCc, and the linear inactive cell region LCi are arrangedalternately to configure the linear unit cell region LC. The trench gateIGBT according to First Embodiment therefore takes a so-called“alternate arrangement system”.

The linear active cell region LCa and the linear hole collector cellregion LCc each have, at the center portion thereof, a contact trench CTalong a second direction (y direction, longer direction) orthogonal tothe first direction (x direction) and the lower end portion of itreaches a P⁺ type body contact region PBC formed in the semiconductorsubstrate.

The linear active cell region LCa has therein an active section LCaa,that is, a region having therein N⁺ type emitter regions NE regularlyarranged in the second direction (y direction, longer direction) and aninactive section LCai, that is, a region (P type body region PB) havingno N⁺ type emitter region NE. These regions are arranged alternately.

The linear hole collector cell region LCc has therein connector trenchgate electrodes (emitter coupling portions) TGc arranged regularly inthe second direction (y direction, longer direction). These connectortrench gate electrodes couple the third linear trench gate electrode TG3and the fourth linear trench gate electrode TG4 to each other. At theintersection between the connector trench gate electrode (emittercoupling portion) TGc and the contact trench CT (P⁺ type body contactregion PBC), the third linear trench gate electrode TG3 and the fourthlinear trench gate electrode TG4 are coupled to each other and are thenelectrically coupled to the emitter electrode EE.

In First Embodiment, the width We of the linear hole collector cellregion LCc and the width Wa of the linear active cell region LCa areequal or substantially equal to each other, which is, however, notessential. Their widths equal or substantially equal to each other,however, have an advantage that the hole distribution becomes uniform.

The linear inactive cell region LCi has therein a P type floating regionPF. In First Embodiment, the P type floating region PF has such astructure that it has a depth greater than that of the lower end portionof the respective trenches having therein first, second, third, andfourth linear trench gate electrodes TG1, TG2, TG3, and TG4 and coversthe lower end portion. Such a structure is not essential but isadvantageous because it facilitates maintenance of a breakdown voltageeven when the width Wi of the linear inactive cell region LCi in thefirst direction (x direction) is made greater than the width Wa of thelinear active cell region LCa in the first direction (x direction). InFirst Embodiment, the width Wa of the linear active cell region LCa inthe first direction (x direction) is made smaller than the width Wi ofthe linear inactive cell region LCi in the first direction (xdirection), which is not essential, but can enhance the IE effect.

The cell formation region CR partially has, outside the peripherythereof, for example, a P type floating region PFp that extends so as tosurround the cell formation region and this P type floating region PFpis electrically coupled to the emitter electrode EE through the contacttrench CT (P⁺ type body contact region PBCp).

In addition, the cell formation region CR has, outside the peripherythereof, for example, a gate wiring GL. The first linear trench gateelectrode TG1 and the second linear trench gate electrode TG2 extendtoward this gate wiring GL from the inside of the cell formation regionCR. A trench gate electrode TGz that couples the respective end portionsof the extensions (that is, gate lead portions TGw) of the first lineartrench gate electrode TG1 and the second linear trench gate electrodeTG2 with each other has electrical coupling to the gate wiring GL via a(gate wiring)-(trench gate electrode) coupling portion GTG. An endtrench gate electrode TGp partitions between the linear inactive cellregion LCi and the peripheral outside of the cell formation region CR.

Next, the cross-sectional structure taken along the line A-A of FIG. 2will be described referring to FIG. 3.

As shown in FIG. 3, an N⁻ type drift region ND occupies the main portionof the semiconductor substrate SS and the semiconductor substrate SShas, on the back surface (second main surface, bottom surface) Sb sidethereof, an N type field stop region Ns contiguous to the N⁻ type driftregion ND. The N type field stop region Ns has an impurity concentrationof, for example, from about 1×10¹⁵ to 1×10¹⁷/cm³.

Further, the N type field stop region Ns has, on the side opposite tothe N⁻ type drift region ND, a P⁺ type first collector region PC1 and aP⁺⁺ type second collector region PC2. The P⁺⁺ type second collectorregion PC2 is on the back surface Sb side of the semiconductor substrateSS in the linear active cell region LCa.

The P⁺⁺ type second collector region PC2 has an impurity concentrationhigher than that of the P⁺ type first collector region PC1. The P⁺ typefirst collector region PC1 has an impurity concentration of, forexample, from about 1×10¹⁶ to 1×10¹⁷/cm³, while the P⁺⁺ type secondcollector region PC2 has an impurity concentration of, for example, fromabout 1×10¹⁷ to 1×10¹⁸/cm³.

The semiconductor substrate SS has, on the back surface Sb thereof, acollector electrode CE to be electrically coupled to the P⁺ type firstcollector region PC1 and the P⁺⁺ type second collector region PC2. Thecollector electrode CE is made of, for example, a stacked film(AlSi/Ti/Ni/Au) obtained by successively stacking aluminum silicon(AlSi), titanium, nickel, and gold successively on the back surface Sbof the semiconductor substrate SS. An electrode material containingaluminum is therefore in contact with the back surface Sb of thesemiconductor substrate SS.

On the other hand, the semiconductor substrate SS has a P type bodyregion PB on almost the entire surface (almost the entire surface in thecell formation region CR) on the side of the surface (first mainsurface, upper surface) Sa of the substrate.

The semiconductor substrate SS has, on the surface Sa side thereof at aboundary between the linear active cell region LCa and the linearinactive cell region LCi, a first trench T1 and a second trench T2. Theyhave, inside thereof, a first linear trench gate electrode TG1 and asecond linear trench gate electrode TG2 via a gate insulating film GI,respectively.

The first linear trench gate electrode TG1 and the second linear trenchgate electrode TG2 have electrical coupling to a gate electrode (thegate electrode GE shown in FIG. 1). The first linear trench gateelectrode TG1 is in the first trench T1 formed in the semiconductorsubstrate SS, while extending from the lower end portion to the upperportion of the trench. Similarly, the second linear trench gateelectrode TG2 is in the second trench T2 formed in the semiconductorsubstrate SS, while extending from the lower end portion to the upperportion of the trench.

The semiconductor substrate SS has, on the surface Sa side thereof at aboundary between the linear hole collector cell region LCc and thelinear inactive cell region LCi, a third trench T3 and a fourth trenchT4. They have therein a third linear trench gate electrode TG3 and afourth linear trench gate electrode TG4 via the gate insulating film GI.

The third linear trench gate electrode TG3 and the fourth linear trenchgate electrode TG4 have electrical coupling to the emitter electrode EE.The third linear trench gate electrode TG3 is the third trench T3 famedin the semiconductor substrate SS, while extending from the lower endportion to the upper portion of the trench. Similarly, the fourth lineartrench gate electrode TG4 is in the fourth trench T4 famed in thesemiconductor substrate SS, while extending from the lower end portionto the upper portion of the trench.

In the linear active cell region LCa, the semiconductor substrate SShas, on the surface side Sa thereof, the N⁺ type emitter region NE andthe contact trench CT has, at the lower end portion thereof, the P⁺ typebody contact region PBC. This P⁺ type body contact region PBC hastherebelow a P⁺ type latch-up prevention region PLP and the P⁺ typelatch-up prevention region PLP has therebelow an N type hole barrierregion NHB. The impurity doped structure in the linear hole collectorcell region Lcc is similar to that of the linear active cell region LCaexcept for omission of the N⁺ type emitter region NE.

In the linear inactive cell region LCi, the semiconductor substrate SShas, on the surface Sa side thereof below the P type body region PB, a Ptype floating region PF deeper than, for example, the first, second,third, and fourth trenches T1, T2, T3, and T4. As shown here, in FirstEmbodiment, the linear hole collector cell region LCc also has, similarto the linear active cell region LCa, an N type hole barrier region NHB,a P⁺ type latch-up prevention region PLP, and the like, but they are notessential. By providing them, however, total balance of the flow ofholes can be maintained.

The semiconductor substrate SS has, on almost the entirety of thesurface Sa thereof, an interlayer insulating film IL made of, forexample, silicon oxide. The interlayer insulating film IL has thereon anemitter electrode EE made of a metal film having, for example, aluminumas a main component and it has coupling to the N⁺ type emitter region NEand the P⁺ type body contact region PBC via the contact trench CT.

The emitter electrode EE further has therein a final passivation filmFPF made of, for example, a polyimide-based organic insulating film.

Next, the cross-sectional structure taken along the line B-B of FIG. 2will be described referring to FIG. 4.

As shown in FIG. 4, in this cross-section, even the linear active cellregion LCa does not have therein the N⁺ type emitter region NE so thatthe linear active cell region LCa and the linear hole collector cellregion LCc are the same in this drawing. The other partial structure isthe same as that described referring to FIG. 3. Needless to say, thisdrawing is similar to FIG. 3 in which the first linear trench gateelectrode TG1 and the second linear trench gate electrode TG2 haveelectrical coupling to a gate electrode (the gate electrode GE shown inFIG. 1), but is different from FIG. 3 in which the third linear trenchgate electrode TG3 and the fourth linear trench gate electrode TG4 haveelectrical coupling to the emitter electrode EE.

Next, the cross-sectional structure taken along the line C-C of FIG. 2will be described referring to FIG. 5.

As shown in FIG. 5, the structure other than the linear hole collectorcell region LCc is similar to that described referring to FIG. 4. Thelinear hole collector cell region LCc has a structure that almost thewhole portion is occupied by only the connector trench gate electrodeTGc (emitter coupling portion).

In First Embodiment, the trench gate IGBT having a “narrow active celltype unit cell” has been described specifically, but needless to say,the description can be applied to not only this but also to a trenchgate IGBT having a “non-narrow active cell type unit cell”.

Further, in First Embodiment, the trench gate IGBT having an “alternatearrangement system” has been described specifically, but needless tosay, the description can be applied to not only this but also to atrench gate IGBT having a “non-alternate arrangement system”.

An example of the main dimensions of each member (refer to FIGS. 1 to 5)of the trench gate IGBT is shown here in order to more specificallyexemplify the structure of the trench gate IGBT.

The width Wa of the linear active cell region LCa is about 1.3 μm andthe width Wi of the linear inactive cell region LCi is about 3.3 μm. Thewidth Wa of the linear active cell region LCa is preferably smaller thanthe width Wi of the linear inactive cell region LCi and a Wi/Wa ratiofalls particularly preferably within a range of, for example, from 2 to3.

The width of the contact trench CT is about 0.3 μm. The width of thefirst, second, third, and fourth trenches T1, T2, T3, and T4 is about0.7 μm (particularly preferably 0.8 μm or smaller) and their depth isabout 3 μm. The depth of the N⁺ type emitter region NE from the surfaceSa of the semiconductor substrate SS is about 0.25 μm, the depth of theP type body region PB (channel region) is about 0.8 μm, the depth of theP⁺ type latch-up prevention region PLP is about 1.4 μm, and the depth ofthe P type floating region PF is about 4.5 μm. The depth of the N typefield stop region Ns from the back surface Sb of the semiconductorsubstrate SS is about 2.0 μm and the depth of the P⁺ type firstcollector region PC1 and the P⁺⁺ type second collector region PC2 isfrom about 0.25 to 1.0 μm.

The thickness of the semiconductor substrate SS is from about 60 to 70μm (the thickness when a breakdown voltage required is about 600 V). Thethickness of the semiconductor substrate SS highly depends on thebreakdown voltage required.

It is therefore, for example, about 120 μm when a breakdown voltagerequired is 1,200 V and about 40 μm when a required breakdown voltage is400 V.

In the following example, members corresponding to them have dimensionsalmost equal to the above-described ones so that a description on themwill not be repeated.

<Advantage of of Trench Gate IGBT>

The advantage of the trench gate IGBT of First Embodiment will bedescribed referring to FIGS. 6 and 7. FIG. 6 is a partially enlargedfragmentary plan view showing an active portion of the semiconductordevice according to First Embodiment. FIG. 7 is a partially enlargedfragmentary cross-sectional view showing a linear active cell regionaccording to First Embodiment.

The trench gate IGBT of First Embodiment is characterized in that apartial region of a collector region famed on the back surface Sb sideof the semiconductor substrate SS is provided with the P⁺⁺ type secondcollector region PC2 having a concentration as relatively high as fromabout 1×10¹⁷ to 1×10¹⁸/cm³.

As described above in the problem (1), it is important not to apply anexcessive collector current in order to ensure load short circuitwithstand, but a reduction in collector current is accompanied by anincrease in ON voltage. Since the P⁺⁺ type second collector region PC2is provided, an increase in field intensity on the back surface Sb sideof the semiconductor substrate SS due to the Kirk effect can besuppressed even if a collector current is increased. It is thereforepossible to ensure the load short circuit withstand.

As described in the problem (2), however, providing the P⁺⁺ type secondcollector region PC2 on the entire surface on the back surface side Sbof the semiconductor substrate SS increases residual carriers on theback surface Sb side of the semiconductor substrate SS at the time ofswitching off and deteriorates the switching off loss performance.

In the trench gate IGBT of First Embodiment, therefore, a partial regionon the back surface Sb side of the semiconductor substrate SS, morespecifically, the linear active cell region LCa is provided with the P⁺⁺type second collector region PC2. This offsets the injected electronswith holes in this P⁺⁺ type second collector region PC2 and suppressesdeterioration in switching off loss performance. FIG. 6 shows a planview in which the P⁺⁺ type second collector region PC2 has beenoverlapped with FIG. 2. FIG. 6 shows the P⁺⁺ type second collectorregion PC2 shaded by hatching.

As shown in FIG. 7, by applying a positive voltage to the linear trenchgate electrode TG electrically coupled to the gate electrode (gateelectrode GE shown in FIG. 1), a channel (inversion layer) is formed inthe P type body region PB on the side surface of the trench T havingtherein the linear trench gate electrode TG and the channel extends inthe depth direction (back surface Sb direction of the semiconductorsubstrate SS). Further, an electron accumulation layer is formed med inthe N type hole barrier region HNB on the side surface of the trench Tand the electron accumulation layer extends in the depth direction (theback surface Sb direction of the semiconductor substrate SS). Electronssupplied from the N⁺ type emitter region NE then flow the channel andthe electron accumulation layer and reach the back surface Sb side ofthe semiconductor substrate SS. The electrons supplied from the surfaceSa side of the semiconductor substrate SS are likely to reach thecollector electrode CE right below and around the interface between thetrench T and the N⁺ type emitter region NE.

In First Embodiment, therefore, the P⁺⁺ type second collector region PC2is provided in the back surface Sb side region of the semiconductorsubstrate SS which many electrons are presumed to reach. Describedspecifically, as shown above in FIGS. 3 to 6, the P⁺⁺ type secondcollector region PC2 is provided in the back surface Sb side region ofthe semiconductor substrate SS including a region right below theinterface between the first trench T1 having therein the first lineartrench gate electrode TG1 and the N⁺ type emitter region NE and a regionright below the interface between the second trench T2 having thereinthe second linear trench gate electrode TG2 and the N⁺ type emitterregion NE. In other words, the P⁺⁺ type second collector region PC2 isprovided so as to include, in plan view, the interface between the firsttrench T1 having therein the first linear trench gate electrode TG1 andthe N⁺ type emitter region NE and the interface between the secondtrench T2 having therein the second linear trench gate electrode TG2 andthe N⁺ type emitter region NE. This makes it possible to realize asemiconductor device equipped with a trench gate IGBT having a low ONvoltage and high load short circuit withstand without deteriorating itsswitching off loss performance.

It is only necessary that a region in which the P⁺⁺ type secondcollector region PC2 is to be formed is, in plan view, at the interfaceor therearound between the first trench T1 having therein the firstlinear trench gate electrode TG1 and the N⁺ type emitter region NE andat the interface or therearound between the second trench T2 havingtherein the second linear trench gate electrode TG2 and the N⁺ typeemitter region NE. In First Embodiment, however, the P⁺⁺ type secondcollector region PC2 is formed in the linear active cell region LCa inconsideration of the alignment margin in the manufacturing steps of thesemiconductor device. The formation region of the P⁺⁺ type secondcollector region PC2 is not limited to the above-described one and amodification example of it will be described later.

<Method of Manufacturing Trench Gate ICBT>

The method of manufacturing the trench gate IGBT according to FirstEmbodiment will next be described referring to FIGS. 8 to 21. FIGS. 8 to21 are fragmentary cross-sectional views showing the manufacturing stepsof the trench gate IGBT according to First Embodiment. The cellformation region will hereinafter be described mainly, while peripheralportions and the like will be understood referring to FIG. 1 as needed.Further, a specific description will be made on the first linear unitcell region LC1 including the linear active cell region LCa and thelinear inactive cell region LCi and the second linear unit cell regionLC2 including the linear hole collector cell region LCc and the linearinactive cell region LCi.

First, as shown in FIG. 8, a semiconductor substrate (in this stage, asubstantially disk-shaped flat and thin semiconductor plate called“wafer”) SS made of an N⁻ type silicon single crystal (for example, aphosphorus concentration of about 2×10¹⁴/cm³) is provided. Thesemiconductor substrate SS is, for example, a 200φ wafer (the waferdiameter may be any of 150φ, 100φ, 300φ, and 450φ). The thickness of thewafer is, for example, about 800 μm (preferably, within a range of fromabout 450 to 1,000 μm). Here, a wafer produced, for example, by FZ(floating zone) method is most suited, but it may be produced by CZ(Czochralski) method.

Next, a resist film (not shown) for introducing an N type hole barrierregion is formed on the entire surface Sa of the semiconductor substrateSS by the method of application or the like. It is patterned by ordinarylithography. An N type impurity is introduced into the surface Sa of thesemiconductor substrate SS, for example, by ion implantation with thepatterned resist film as a mask to form an N type hole barrier regionNHB. Preferred examples of the condition employed for this ionimplantation include the following condition: using phosphorus as an ionspecies, a dose of about 6×10¹²/cm², and implantation energy of about 80KeV. The resist film which becomes unnecessary is then removed by ashingor the like.

Next, a resist film (not shown) for introducing a P type floating regionis formed on the entirety of the surface Sa of the semiconductorsubstrate SS by the method of application or the like, followed bypatterning using ordinary lithography. A P type impurity is introducedinto the surface Sa of the semiconductor substrate SS, for example, byion implantation with the patterned resist film as a mask to form a Ptype floating region PF. Preferred examples of the condition employedfor this ion implantation include the following condition: boron used asan ion species, a dose of about 3.5×10¹³/cm², and implantation energy ofabout 75 KeV. Then, the resist film that becomes unnecessary is removedby ashing or the like. Simultaneously with the introduction of the Ptype floating region PF, for example, a cell periphery junction regionand a floating field ring are introduced.

Next, a hard mask HM made of, for example, silicon oxide is formed onthe entirety of the surface Sa of the semiconductor substrate SS, forexample, by CVD (chemical vapor deposition). The hard mask HM has athickness of, for example, about 450 nm.

Next, as shown in FIG. 9, a resist film (not shown) for hard mask filmprocessing is formed on the entirety of the surface Sa of thesemiconductor substrate SS by the method of application or the like andthe resulting film is patterned by ordinary lithography. The hard maskfilm HM is patterned, for example, by dry etching with the patternedresist film as a mask. Then, the resist film that becomes unnecessary isremoved by ashing or the like.

Next, as shown in FIG. 10, using the patterned hard mask HM, forexample, anisotropic dry etching is performed to form first, second,third, and fourth trenches T1, T2, T3, and T4, respectively. Preferredexamples of the gas for this anisotropic dry etching include aCl₂/O₂-based gas.

By wet etching using, for example, a hydrofluoric acid-based etchant,the hard mask HM that becomes unnecessary is removed.

Next, as shown in FIG. 11, extending diffusion (for example, at 1200° C.for about 30 minutes) of the P type floating region PF and the N typehole barrier region NHB is performed. By this diffusion, the P typefloating region PF becomes deeper than the lower end portions of thefirst, second, third, and fourth trenches T1, T2, T3, and T4 in whichfirst, second, third, and fourth linear trench gate electrodes TG1, TG2,TG3, and TG4 are to be formed, respectively, and it covers the lower endportions. A region of the semiconductor substrate SS not having thereinthe P type floating region PF and the N type hole barrier region NHBbecomes an N⁻ type drift region ND.

Next, for example, by thermal oxidation, a gate insulating film GI isformed on the surface Sa of the semiconductor substrate SS and on theentire surface of the inner wall of the first, second, third, and fourthtrenches T1, T2, T3, and T4. The gate insulating film GI has a thicknessof, for example, about 0.12 μm.

Next, as shown in FIG. 12, a phosphorus-doped polycrystalline silicon(doped poly-silicon) film DPS is formed, for example, by CVD on thesurface Sa of the semiconductor substrate SS and inside the first,second, third, and fourth trenches T1, T2, T3, and T4. Thepolycrystalline silicon film DPS has a thickness of, for example, about0.6 μm.

Next, the polycrystalline silicon film DPS is etched back, for example,by dry etching to form a first linear trench gate electrode TG1 insidethe first trench T1, a second linear trench gate electrode TG2 insidethe second trench T2, a third linear trench gate electrode TG3 insidethe third trench T3, and a fourth linear trench gate electrode TG4 inthe fourth trench T4. Preferred examples of the gas used in this etchback include SF₆.

Next, as shown in FIG. 13, a resist film (not shown) for introducing a Ptype body region is formed by the method of application or the like onthe entirety of the surface Sa of the semiconductor substrate SS. Thefilm is then patterned by ordinary lithography. A P type impurity isintroduced into the entire surface of the cell formation region CR andanother necessary portion, for example, by ion implantation with thepatterned resist film as a mask to form a P type body region PB.Preferred examples of the condition employed for this ion implantationinclude the following condition: boron used as an ion species, a dose ofabout 3×10¹³/cm², and implantation energy of about 75 KeV. Then, theresist film that becomes unnecessary is removed by ashing or the like.

A resist film (not shown) for introducing an N⁺ type emitter region isformed by the method of application or the like on the entirety of thesurface Sa of the semiconductor substrate SS. An N type impurity isintroduced into the entirety of the upper surface of the P type bodyregion PB in the linear active cell region LCa, for example, by ionimplantation with the patterned resist film as a mask to form an N⁺ typeemitter region NE. Preferred examples of the condition employed for thision implantation include the following condition: arsenic used as an ionspecies, a dose of about 5×10¹⁵/cm², and implantation energy of about 80KeV. The resist film that becomes unnecessary is then removed by ashingor the like.

Next, as shown in FIG. 14, for example, a PSG (phosphosilicate glass)film is famed on the entirety of the surface Sa of the semiconductorsubstrate SS as an interlayer insulating film IL, for example, by CVD.The interlayer insulating film IL has a thickness of about 0.6 μm.Preferred examples of the material of this interlayer insulating film ILinclude, in addition to a PSG film, a BPSG (borophosphosilicate glass)film, an NSG (non-doped silicate glass) film, and an SOG (spin-on-glass)film, and a composite film thereof.

Next, as shown in FIG. 15, a resist film (not shown) for forming acontact trench is formed by the method of application or the like on theentire surface of the interlayer insulating film IL and is thenpatterned by ordinary lithography. A contact trench CT is formed, forexample, by anisotropic etching with the patterned resist film as amask. Preferred examples of the gas used for this anisotropic dryetching include Ar/CHF₃/CF₄-based gas. Then, the resist film thatbecomes unnecessary is removed by asking or the like.

Next, the contact trench CT (or contact hole) is extended in thesemiconductor substrate SS, for example, by anisotropic dry etching.Preferred examples of the gas for this anisotropic dry etching include aCl₂/O₂-based gas.

Next, as shown in FIG. 16, a P⁺ type body contact region PBC is formedby the ion implantation of a P type impurity, for example, through thecontact trench CT. Preferred examples of the condition employed for thision implantation include the following condition: boron fluoride (BF₂)used as an ion species, a dose of about 5×10¹⁵/cm², and implantationenergy of about 80 KeV.

Similarly, a P⁺ type latch-up prevention region PLP is formed, forexample, by the ion implantation of a P type impurity through thecontact trench CT. Preferred examples of the condition employed for thision implantation include the following condition: boron used as an ionspecies, a dose of about 5×10¹⁵/cm², and implantation energy of about 80KeV.

Next, as shown in FIG. 17, an emitter electrode EE is formed. Describedspecifically, it is formed, for example, in the following procedure.First, a titanium tungsten (TiW) film is farmed as a barrier metal filmon the entirety of the surface Sa of the semiconductor substrate SS, forexample, by sputtering. The titanium tungsten film has a thickness of,for example, about 0.2 μm. A major portion of titanium in the titaniumtungsten film transfers to the silicon interface by the heat treatmentconducted later to form a silicide and this contributes to improvementin the contact characteristics. These procedures are complicated so thatthey are not shown in the drawing.

Next, silicide annealing, for example, at 600° C. for about 10 minutesis performed in a nitrogen atmosphere. Then, an aluminum-based metalfilm (for example, containing aluminum and several % of silicon) isformed on the entire surface of the barrier metal film, for example, bysputtering so as to fill the contact trench CT with it. Thealuminum-based metal film has a thickness of, for example, about 5 μm.

Next, a resist film (not shown) for forming an emitter electrode isformed on the entirety of the surface Sa of the semiconductor substrateSS by the method of application or the like and is then patterned byordinary lithography. The emitter electrode EE made of thealuminum-based metal film and the barrier metal film is patterned, forexample, by dry etching with the thus-patterned resist film as a mask.Preferred examples of the gas used for this dry etching include aCl₂/BCl₃-based gas. The resist film that becomes unnecessary is thenremoved by ashing or the like.

Next, a final passivation film FPF made of an organic film or the likehaving, for example, polyimide as a main component is formed on theemitter electrode EE. The final passivation film FPF has a thickness of,for example, about 2.5 μm.

Next, a resist film (not shown) for forming an opening portion is formedon the entirety of the surface Sa of the semiconductor substrate SS bythe method of application or the like, followed by ordinary lithographyto pattern the film. The final passivation film FPF is patterned, forexample, by dry etching with the patterned resist film as a mask to openan emitter pad EP or the like shown above in FIG. 1. Then, the resistfilm that becomes unnecessary is removed by ashing or the like.

Next, as shown in FIG. 18, the back surface Sb of the semiconductorsubstrate SS is ground by back grinding treatment and the thickness isreduced from about 800 μm to, for example, from about 30 to 200 μm asneeded. When the breakdown voltage is, for example, about 600 V, thefinal thickness is about 60 μm, and when the breakdown voltage is about1,200 V, the final thickness is about 120 μm; and when the breakdownvoltage is about 1,800 V, the final thickness is about 180 μm. Ifnecessary, chemical etching or the like is performed to remove thedamage from the back surface Sb.

Next, an N type field stop region Ns is formed by introducing an N typeimpurity into the entirety of the back surface Sb of the semiconductorsubstrate SS, for example, by ion implantation. Preferred examples ofthe condition employed for this ion implantation include the followingcondition: phosphorus used as an ion species, a dose of about5×10¹²/cm², and implantation energy of about 350 KeV.

Next, as shown in FIG. 19, a P⁺ type first collector region PC1 isformed, for example, by introducing a P type impurity into the entiretyof the back surface Sb of the semiconductor substrate SS, for example,by ion implantation. Preferred examples of the condition employed forthis ion implantation include the following condition: boron used as anion species, a dose of about 7×10¹²/cm², and implantation energy ofabout 40 KeV.

Next, as shown in FIG. 20, a resist mask R1 for introducing a P⁺⁺ typesecond collector region is faulted on the entirety of the back surfaceSb of the semiconductor substrate SS by the method of application or thelike, followed by ordinary lithography to pattern it. A P type impurityis introduced into the back surface Sb of the semiconductor substrateSS, for example, by ion implantation with the patterned resist mask R1as a mask to form a P⁺⁺ type second collector region PC2. Preferredexamples of the condition employed for this ion implantation include thefollowing condition: boron used as an ion species, a dose of about5×10¹³/cm², and implantation energy of about 40 KeV. The resist mask R1that becomes unnecessary is then removed by ashing or the like. Foractivation of the impurity, the back surface Sb of the semiconductorsubstrate SS is subjected to laser annealing or the like if necessary.The P⁺⁺ type second collector region PC2 is famed in the linear activecell region LCa (refer to FIG. 6 or the like).

Next, as shown in FIG. 21, a collector electrode CE is formed on theentirety of the back surface Sb of the semiconductor substrate SS bystacking aluminum silicon (AlSi), titanium, nickel, and goldsuccessively, for example, by sputtering. Then, the semiconductorsubstrate SS is divided into chip regions by dicing or the like,followed by sealing in a package as needed to form a semiconductordevice having a trench gate IGBT.

Thus, in the trench gate IGBT of First Embodiment, the collector regionformed on the back surface Sb side of the semiconductor substrate SS iscomprised of a relatively lightly-doped P⁺ type first collector regionPC1 and a relatively heavily-doped P⁺⁺ type second collector region PC2.The P⁺⁺ type second collector region PC2 is provided in a regionincluding, in plan view, the boundary between the first trench T1 havingtherein the first linear trench gate electrode TG1 and the N⁺ typeemitter region NE and the boundary between the second trench T2 havingtherein the second linear trench gate electrode TG2 and the N⁺ typeemitter region NE. This makes it possible to realize a semiconductordevice equipped with a trench gate IGBT having a low ON voltage and highload short circuit withstand without deteriorating its switching offloss performance.

(Modification Example 1)

A semiconductor device having a trench gate IGBT according toModification Example 1 of First Embodiment will be described referringto FIG. 22. FIG. 22 is a partially enlarged fragmentary plan viewshowing an active portion of the semiconductor device according toModification Example 1 of First Embodiment and it is a plan viewobtained by overlapping a P⁺⁺ type second collector region with FIG. 2.FIG. 22 shows the P⁺⁺ type second collector region shaded by hatching.

A difference from First Embodiment is the area of the P⁺⁺ type secondcollector region PC2. The P⁺⁺ type second collector region PC2 in FirstEmbodiment is provided in the linear active cell region LCa.

However, in Modification Example 1, as shown in FIG. 22, the P⁺⁺ typesecond collector region PC2 is extended to the linear inactive cellregion LCi. The P⁺⁺ type second collector region PC2 is provided, forexample, in the first linear unit cell region LC1 comprised of thelinear active cell region LCa which is at the center thereof and a pairof half-width linear inactive cell regions LCi surrounding the activecell region.

As shown above in FIG. 7, electrons supplied from the N⁺ type emitterregion NE flow through the channel and the electron accumulation layerand reach the back surface side Sb of the semiconductor substrate SS.Many of the electrons supplied from the surface Sa side of thesemiconductor substrate SS therefore reach the collector electrode CEright below and around the interface between the first trench T1 havingtherein the first linear trench gate electrode TG1 and the N type holebarrier region NHB and right below and around the interface between thesecond trench T2 having therein the second linear trench gate electrodeTG2 and the N type hole barrier region NHB. Some electrons, however,gradually diffuse, with a certain angle, in a normal line direction ofthe back surface Sb of the semiconductor substrate SS while theytransfer in the N⁻ type drift region ND.

In Modification Example 1, therefore, the P⁺⁺ type second collectorregion PC2 is made wider than that in First Embodiment in order toenhance effectiveness of offsetting the electrons supplied from the N⁺type emitter region NE with holes of the P⁺⁺ type second collectorregion PC2. The switching off loss performance is, however, presumed tobecome inferior to that of First Embodiment by making the P⁺⁺ typesecond collector region PC2 wider than that of First Embodiment.

(Modification Example 2)

A semiconductor device having a trench gate IGBT according toModification Example 2 of First Embodiment will be described referringto FIG. 23. FIG. 23 is a partially enlarged fragmentary plan viewshowing an active portion of the semiconductor device according toModification Example 2 of First Embodiment and it is a plan viewobtained by overlapping a P⁺⁺ type second collector region with FIG. 2.FIG. 23 shows the P⁺⁺ type second collector region shaded by hatching.

A difference from First Embodiment is the area of the P⁺⁺ type secondcollector region PC2. In First Embodiment, the P⁺⁺ type second collectorregion PC2 is provided in the linear active cell region LCa.

In Modification Example 2, however, as shown in FIG. 23, the P⁺⁺ typesecond collector region PC2 is provided, in plan view, only in the N⁺type emitter region NE and therearound.

As shown in FIG. 7, electrons supplied from the N⁺ type emitter regionNE flow through the channel and the electron accumulation layer andreach the back surface Sb side of the semiconductor substrate SS. Manyof the electrons supplied from the surface Sa side of the semiconductorsubstrate SS therefore reach the collector electrode CE right below andaround the interface between the first trench T1 having therein thefirst linear trench gate electrode TG1 and the N type hole barrierregion NHB and right below and around the interface between the secondtrench T2 having therein the second linear trench gate electrode TG2 andthe N type hole barrier region NHB.

In Modification Example 2, the P⁺⁺ type second collector region PC2 istherefore provided only in a region which many of electrons suppliedfrom the N⁺ type emitter region NE are presumed to reach. The resultingtransistor is presumed to have improved switching off loss performanceand, due to the Kirk effect, have reduced load short circuit withstandby making the P⁺⁺ type second collector region PC2 narrower than that ofFirst Embodiment.

(Modification Example 3)

A semiconductor device having a trench gate IGBT according toModification Example 3 of First Embodiment will next be describedreferring to FIGS. 24A, 24B, and 25. FIGS. 24A and 24B are surface-sideand back-surface-side fragmentary plan views of the semiconductor deviceaccording to Modification Example 3 of First Embodiment, respectively.FIG. 24A is a plan view obtained by overlapping a P⁺ type firstcollector region with FIG. 1 and FIG. 24B is a plan view of a collectorelectrode viewed through from the back surface side of the semiconductorsubstrate. FIGS. 24A and 24B show the P⁺ type first collector regionshaded by hatching. FIG. 25 is a partially-enlarged fragmentaryschematic cross-sectional view of the semiconductor device according toModification Example 3 of First Embodiment.

Differences from First Embodiment are the area of the P⁺ type firstcollector region PC1 and presence or absence of the P⁺⁺ type secondcollector region PC2. Described specifically, in First Embodiment, thesemiconductor substrate SS has, on the entire surface on the backsurface Sb thereof, the P⁺ type first collector region PC1 and has, inthe linear active cell region LCa, the P⁺⁺ type second collector regionPC2.

In Modification Example 3, however, as shown in FIG. 24A, the P⁺ typefirst collector region PC1 is formed in a region overlapping, in planview, with the emitter electrode EE and the gate electrode GE withoutforming the P⁺⁺ type second collector region PC2. In other words, asshown in FIG. 25, the P⁺ type first collector region PC1 is formed onlyon the back surface Sb side of the semiconductor substrate SS in thecell formation region and the P⁺ type first collector region PC1 is notformed in the other region. As shown in FIG. 24B, therefore, the P⁺ typefirst collector region PC1 is exposed from the back surface Sb of thesemiconductor substrate SS in the cell formation region, while the Ntype field stop region Ns is exposed from the back surface Sb of thesemiconductor substrate SS in a region other than the cell formationregion.

As shown above in FIG. 7, electrons supplied from the N⁺ type emitterregion NE flow through the channel and the electron accumulation layerand reach the back surface Sb side of the semiconductor substrate SS.Electrons supplied from the surface Sa side of the semiconductorsubstrate SS therefore reach the collector electrode CE in the cellformation region. Electrons are, on the other hand, not supplied fromthe peripheral portion of the semiconductor chip SC so that there is noneed of unnecessarily forming a PNP structure on the back surface Sb ofthe semiconductor substrate SS and thereby leaving a fear of latch-up.

In Modification Example 3, therefore, the P⁺ type first collector regionPC1 is provided only on the back surface Sb side of the semiconductorsubstrate SS in the cell formation region. However, the transistor thusobtained is presumed to become inferior in switching off lossperformance to that of First Embodiment. When the concentration in theP⁺ type first collector region PC1 is low, the load short circuitwithstand may decrease due to the Kirk effect so that in ModificationExample 3, the concentration in the P⁺ type first collector region PC1may be made higher than that in First Embodiment.

(Modification Example 4)

A semiconductor device having a trench gate IGBT according toModification Example 4 of First Embodiment will next be describedreferring to FIGS. 26 and 27. FIG. 26 is a surface-side fragmentary planview showing the semiconductor device according to Modification Example4 of First Embodiment and it is a plan view obtained by overlapping theP⁺ type first collector region with FIG. 1. In FIG. 26, the P⁺ typefirst collector region is shaded by hatching. FIG. 27 is a partiallyenlarged fragmentary plan view of an active portion of the semiconductordevice according to Modification Example 4 of First Embodiment and it isa plan view obtained by overlapping the P⁺⁺ type second collector regionwith FIG. 2. In FIG. 27, the P⁺⁺ type second collector region is shadedby hatching.

A difference from First Embodiment is the area of the P⁺ type firstcollector region PC1. Described specifically, in First Embodiment, thesemiconductor substrate SS has, on the entire surface on the backsurface Sb side thereof, the P⁺ type first collector region PC1 and has,in the linear active cell region LCa, the P⁺⁺ type second collectorregion PC2.

In Modification Example 4, however, as shown in FIG. 26, the P⁺ typefirst collector region PC1 is formed in a region overlapping, in planview, with the emitter electrode EE and the gate electrode GE. As shownin FIG. 27, on the other hand, the P⁺⁺ type second collector region PC2is provided in the linear active cell region LCa similarly to FirstEmbodiment. This means that the P⁺ type first collector region PC1 isexposed from the back surface Sb of the semiconductor substrate SS inthe cell formation region and the N type field stop region Ns is exposedfrom the back surface Sb of the semiconductor substrate SS in a regionother than the cell formation region as in FIG. 24B, but a plurality ofthe P⁺⁺ type second collector regions PC2 is exposed in the P⁺ typefirst collector region PC1.

As shown above in FIG. 7, electrons supplied from the N⁺ type emitterregion NE flow through the channel and the electron accumulation layerand reach the back surface Sb side of the semiconductor substrate SS.Electrons supplied from the surface Sa side of the semiconductorsubstrate SS therefore reach the collector electrode CE in the cellformation region. On the other hand, no electrons are supplied from theperipheral portion of the semiconductor chip SC so that there is no needof unnecessarily forming a PNP structure on the back surface Sb of thesemiconductor substrate SS and thereby leaving a fear of latch-up.

In Modification Example 4, the P⁺ type first collector region PC1 andthe P⁺⁺ type second collector region PC2 are therefore provided only onthe back surface Sb side of the semiconductor substrate SS in the cellformation region.

(Second Embodiment)

A trench gate IGBT according to Second Embodiment will next be describedreferring to FIGS. 28 and 29. FIG. 28 is a partially enlargedfragmentary plan view of an active region of a semiconductor deviceaccording to Second Embodiment. FIG. 29 is a fragmentary cross-sectionalview taken along the line D-D shown in FIG. 28.

The trench gate IGBT described herein is a so-called EGE type trenchgate IGBT in which three trench gate electrodes are arranged with aspace between any two of them, the trench gate electrode at the centerof them is electrically coupled to a gate electrode, and two trench gateelectrodes arranged at both ends are electrically coupled to an emitterelectrode. The trench gate IGBT of the present embodiment is differentfrom that of First Embodiment in the respective structures of a linearactive cell region LCa, a linear inactive cell region LCi, and a linearhole collector cell region LCc. In the following description, only aportion different from the trench gate IGBT of First Embodiment will bedescribed in principle.

As shown in FIG. 28, a linear unit cell region LC according to SecondEmbodiment is comprised of a linear hybrid cell region LCh andhalf-width linear inactive cell regions LCi on both sides thereof. Thewidth Wh of the linear hybrid cell region LCh is narrower than the widthWi of the linear inactive cell region LCi.

The linear hybrid cell region LCh is comprised of a first linear hybridsub-cell region LCh1 and a second linear hybrid sub-cell region LCh2which are plane symmetrical to each other. The first linear hybridsub-cell region LCh1 is a hybrid cell obtained by integrating a righthalf cell of the linear active cell region LCa with a left half cell ofthe linear hole collector cell region LCc, each shown above in FIG. 2.On the other hand, the second linear hybrid sub-cell region LCh2 is ahybrid cell obtained by integrating a left half cell of the linearactive cell region LCa with a right half cell of the linear holecollector cell region LCc, each shown above in FIG. 2.

In other words, the linear hybrid cell region LCh is a combination ofthe first linear hybrid sub-cell region LCh1 and the second linearhybrid sub-cell region LCh2 famed so as to have a first linear trenchgate electrode TG1 electrically coupled to the gate electrode (gateelectrode GE shown above in FIG. 1) at the center. In Second Embodiment,therefore, the width Wh1 of the first linear hybrid sub-cell region LCh1is equal or substantially equal to the width Wh2 of the second linearhybrid sub-cell region LCh2.

A second linear trench gate electrode TG2 and a third linear trench gateelectrode TG3 to be electrically coupled to an emitter electrode EE areplaced on two respective sides having therebetween the linear inactivecell region LCi. Intercoupling is therefore achieved by providing, inaddition to an end trench gate electrode TGp, a coupling gate lead pad(emitter coupling portion) TGx made of a polycrystalline film which isof the same layer as the second linear trench gate electrode TG2 and thethird linear trench gate electrode TG3. A contact trench CT thatelectrically couples the second linear trench gate electrode TG2 and thethird linear trench gate electrode TG3 to the emitter electrode EE isplanarly included in the coupling gate lead pad (emitter couplingportion) TGx. Such a structure enables further improvement in couplingreliability.

Next, the cross-sectional structure taken along the line D-D of FIG. 28will next be described referring to FIG. 29.

As shown in FIG. 29, an N⁻ type drift region ND occupies the mainportion of the semiconductor substrate SS and the semiconductorsubstrate SS has, on the back surface Sb side thereof, an N type fieldstop region Ns contiguous to the N⁻ type drift region ND. The N typefield stop region Ns has an impurity concentration of, for example, fromabout 1×10¹⁵ to 1×10¹⁷/cm³.

Further, the N type field stop region Ns has, on the side opposite tothe N type drift region ND, a P⁺ type first collector region PC1 and aP⁺⁺ type second collector region PC2 which are contiguous to the N typefield stop region Ns. The P⁺⁺ type second collector region PC2 isprovided in a half width of the first linear hybrid sub-cell region LCh1and a half width of the second linear hybrid cell region LCh2, betweenwhich lies the first trench T1 having therein the first linear trenchgate electrode TG1. The impurity concentration of the P⁺⁺ type secondcollector region PC2 is higher than that of the P⁺ type first collectorregion PC1. The P⁺ type first collector region PC1 has an impurityconcentration of, for example, from about 1×10¹⁶to 1×10¹⁷/cm³ and theP⁺⁺ type second collector region PC2 has an impurity concentration of,for example, from about 1×10′⁷ to 1×10¹⁸/cm³.

Further, the semiconductor substrate SS has, on the back surface Sbthereof, a collector electrode CE to be electrically coupled to the P⁺type first collector region PC1 and the P⁺⁺ type second collector regionPC2.

The semiconductor substrate SS has, on almost the entirety of thesurface Sa side thereof (almost the entire surface in the cell formationregion CR), a P type body region PB.

The semiconductor substrate SS has, on the surface Sa side thereof at aboundary between the first linear hybrid sub-cell region LCh1 and thesecond linear hybrid sub-cell region LCh2, a first trench T1. It has,inside thereof, the first linear trench gate electrode TG1 via a gateinsulating film GI.

The first linear trench gate electrode TG1 has electrical coupling to agate electrode (the gate electrode GE shown above in FIG. 1). In thefirst trench T1 formed in the semiconductor substrate SS, the firstlinear trench gate electrode TG1 extends from the lower end portion tothe upper portion of the trench.

On the other hand, the semiconductor substrate SS has, on the surface Saside at a boundary between the linear hybrid cell region LCh and thelinear inactive cell region LCi, a second trench T2 and a third trenchT3. They have, inside thereof, the second linear trench gate electrodeTG2 and the third linear trench gate electrode TG3 via the gateinsulating film GI, respectively.

The second linear trench gate electrode TG2 and the third linear trenchgate electrode TG3 each have electrical coupling to the emitterelectrode EE. In the second trench T2 famed in the semiconductorsubstrate SS, the second linear trench gate electrode TG2 extends fromthe lower end portion to the upper portion of the trench. Similarly, inthe third trench T3 formed in the semiconductor substrate SS, the thirdlinear trench gate electrode TG3 extends from the lower end portion tothe upper portion of the trench.

In the first linear hybrid sub-cell region LCh1 and the second linearhybrid sub-cell region LCh2, the semiconductor substrate SS has, on thesurface Sa side thereof and only on the side of the first linear trenchgate electrode TG1, an N⁺ type emitter region NE and the contact trenchCT has, at the lower end portion thereof, a type body contact regionPBC. This P⁺ type body contact region PBC has therebelow a P⁺ typelatch-up prevention region PLP. The P⁺ type latch-up prevention regionPLP has therebelow an N type hole barrier region NHB.

In the linear inactive cell region LCi, the semiconductor substrate SShas, on the surface Sa side thereof, a P type floating region PF deeperthan, for example, the first, second, and third trenches T1, T2, and T3below the P type body region PB.

The semiconductor substrate SS has, on almost the entirety of thesurface Sa, an interlayer insulating film IL made of, for example,silicon oxide. The interlayer insulating film IL has, thereon, anemitter electrode EE made of a metal film having, for example, aluminumas a main component thereof. It has coupling to the N⁺ type emitterregion NE and the P⁺ type body contact region PBC via the contact trenchCT.

The emitter electrode 3E further has thereon a final passivation filmFPF made of, for example, a polyimide-based organic insulating film.

As described above in First Embodiment (refer to FIG. 7), when apositive voltage is applied to the first linear trench gate electrodeTG1 electrically coupled to the gate electrode, a channel (inversionlayer) is formed in the P type body region PB on the side surface of thefirst trench T1 having therein the first linear trench gate electrodeTG1 and the channel extends in the depth direction (the back surface Sbdirection of the semiconductor substrate SS). Further, an accumulationlayer is formed in the N type hole barrier region HHB on the sidesurface of the first trench T1 and it extends in the depth direction(the back-surface Sb direction of the semiconductor substrate SS).Electrons supplied from the N⁺ type emitter region NE flow through thechannel and electron accumulation layer and reach the back surface Sbside of the semiconductor substrate SS. Electrons supplied from thesurface Sa side of the semiconductor substrate SS are likely to reachthe collector electrode CE right below and around the interface betweenthe first trench T1 and the N type hole barrier region NHB.

In Second Embodiment, therefore, a P⁺⁺ type second collector region PC2is provided in the back surface Sb side region of the semiconductorsubstrate SS including a region right below the interface between thefirst trench T1 having therein the first linear trench gate electrodeTG1 and the N type ball barrier region NHB. In other words, a P⁺⁺ typesecond collector region PC2 is provided so as to include, in plan view,the interface between the first trench T1 having therein the firstlinear trench gate electrode TG1 and the N⁺ type emitter region NE. Thisenables the present embodiment to produce an advantage almost similar tothat of First Embodiment and makes it possible to achieve asemiconductor device equipped with a trench gate IGBT having a low ONvoltage and high load short circuit withstand without deteriorating itsswitching-off loss performance.

The invention made by the present inventors has been describedspecifically based on some embodiments. It is needless to say that theinvention is not limited to or by these embodiments but can be changedin various ways without departing from the gist of the invention.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising the steps of: (a) providing a semiconductor substrate of afirst conductivity type having a first main surface and a second mainsurface on a side opposite to a side of the first main surface; (b)forming a first trench and a second trench each having a first depthfrom the first main surface of the semiconductor substrate, the firstand second trenches spaced apart from each other; (c) forming, in thefirst trench, a first trench gate electrode having a first conductivefilm via a first gate insulating film having a first insulating film,and forming, in the second trench, a second trench gate electrode havingthe first conductive film via a second gate insulating film having thefirst insulating film; (d) forming a first semiconductor region of asecond conductivity type different from the first conductivity type, thefirst semiconductor region having, from the first main surface of thesemiconductor substrate, a second depth smaller than the first depth;(e) forming, in the first semiconductor region, a second semiconductorregion of the first conductivity type, the second semiconductor regionhaving, from the first main surface of the semiconductor substrate, athird depth smaller than the second depth so as to be contiguous to afirst side surface of the first trench; (f) forming an interlayerinsulating film over the first main surface of the semiconductorsubstrate, and then forming, over the interlayer insulating film, afirst electrode to be electrically coupled to the first trench gateelectrode and the second trench gate electrode, and a second electrodeto be electrically coupled to the first semiconductor region and thesecond semiconductor region; (g) grinding the semiconductor substratefrom the side of the second main surface; (h) forming a thirdsemiconductor region on the side of the second main surface by ionimplantation of an impurity of the second conductivity type into thesecond main surface of the semiconductor substrate; (i) forming a resistfilm over the second main surface of the semiconductor substrate andthen patterning the resist film; (j) forming a fourth semiconductorregion on the side of the second main surface by ion implantation of animpurity of the second conductivity type into the second main surface ofthe semiconductor substrate, with the patterned resist film as a mask;and (k) forming a third electrode that electrically couples the thirdsemiconductor region to the fourth semiconductor region over the secondmain surface of the semiconductor substrate, wherein the fourthsemiconductor region is formed in a region including, in plan view, aninterface between the first trench and the second semiconductor region,and wherein the first conductivity type is N-type and the secondconductivity type is P-type.
 2. The method of manufacturing asemiconductor device according to claim 1, wherein the fourthsemiconductor region is formed in a region overlapping, in plan view,the second semiconductor region.
 3. The method of manufacturing asemiconductor device according to claim 1, wherein the thirdsemiconductor region has an impurity concentration of from 1×10¹⁶ to1×10¹⁷/cm³ and the fourth semiconductor region has an impurityconcentration of from 1×10¹⁷to 1×10¹⁸/cm³.
 4. The method ofmanufacturing a semiconductor device according to claim 1, wherein bygrinding in the step (g), the thickness of the semiconductor substrateis reduced to 30 to 200 μm.